The scale on a map is 4cm : 2km. If the distance between two cities is 16km, how far apart in cm are the two cities on the map?
Solution: The scale means that every 4cm on the map corresponds to an actual distance of 2km. An actual distance of 16km is the same as 8 $\cdot$ 2km. The distance between the two cities on the map is 8 $\cdot$ 4cm, or 32cm.